A pulse motor (or a stepping motor) is generally used as means for rotating a rotary member by a prescribed rotational angle, e.g. a roller of a paper feeder unit of a copying machine. The rotary shaft of the pulse motor changes its rotational angle in proportion to the number of pulses inputted. When the roller of the paper feeder unit is connected to the rotary shaft of the pulse motor, the roller can be rotated by prescribed angles.
However, when the pulse motor is continuously operated, accumulated error occurs and a rotational lag occurs. Therefore, precision machines should have a correction circuit, etc. and in the manufacturing process, the conventional field core has been formed like a cup so as to close the magnetic circuit of an electromagnetic coil. To form a cup-like shape, drawing work or boring work is required, so that there is also a problem of lower manufacturing efficiency.